(1) Field of the Invention
This invention relates to the application and delivery of laser energy to ocular tissue for controlled removal of various components thereof. More particularly, this invention pertains to surgical apparatus and procedures involving ultraviolet excimer lasers or infrared lasers in combination with fiberoptic elements for effecting photoablation of ocular and periocular tissue, especially in connection with cataract removal or treatment of eye diseases, such as glaucoma, vitreous humor abnormalities or tear duct ostructions. The main thrust of this invention concerns the coupling of ultraviolet excimer or infrared lasers to fiberoptic elements which have been passed through perforations in eyeball encapsulating and periocular tissue--for example, the cornea or sclera, after paracentesis thereof--and then advanced transocularly so that the penetrating end is juxtaposed adjacent the diseased tissue (cataractous lens, trabecular meshwork or angle structures, vitreous membranes, occluded tear duct passages or the like), whereby the coherent (UV or infrared) radiation is delivered through the fiber and the emission therefrom is directed immediately and precisely upon the target sites.
(2) Prior Art
(a) Cataract Removal
Cataract is a disease of the eye in which the crystalline lens or its capsule becomes opaque or clouded. Current techniques for removing cataractous tissue require incisions in the cornea large enough to physically withdraw the lens, which can measure upwards of 10 mm., or the use of ultrasound generating devices to pulverize the lens in situ. The latter instance, in which a corneal incision of at least 3 mm. is required, imposes a potential risk of damage to adjacent intraocular structures as a result of dispersement of ultrasonic energy within the eye's fluid medium and/or from the free floating lens particles created during the fragmentation process. Both of these latter procedures require the use of suture materials to close the corneal wounds created to allow access to the interior of the eye.
With the development of intraocular lenses capable of being inserted through small surgical wound apertures, it has become possible to manipulate through a wound small enough to be self-sealing, making suture closure no longer mandatory. By avoiding the need for large iatrogenic wounds and the necessity of sutures, healing becomes more rapid and the risks of surgically induced astigmatism are reduced as are the recovery and rehabilitation periods.
Accordingly, it is desirable to remove the lens tissue itself in such a way as to minimize corneal incision size and in a manner least disruptive to the neighboring tissue, thereby delimiting any induced inflammatory response and its sequelae.
(b) Glaucoma surgery
Glaucoma refers to a series of relatively common eye disorders in which pressure within the eye is sufficiently high as to result in damage to sensitive intraocular structures, including the retina and optic nerve. Glaucomas are classified as primary (including chronic open angle glaucoma, angle closure glaucoma, mixed mechanism glaucoma and infantile glaucoma) and secondary (related to other diseases of the eye). The elevation of intraocular pressure ultimately leads to irreversible destruction of the optic nerve. The clinical symptoms, which are not readily recognized in the early stages, are characterized mainly by a slow, relentless, progressive narrowing of the field of vision, and decrement in visual integration processing, including diminished dark adaptation. In the absence of treatment, the eventual outcome is total loss of vision together with severe eye pain.
Present surgical techniques to lover intraocular pressure (recruited when medication has proven inadequate to decrease fluid flow into the eye or to increase fluid outflow) include procedures enabling fluid to drain from within the eye to extraocular sites. However, these drainage or "filtering" procedures, as they are called, not only induce risk to the lens causing cataract, but often fail by virtue of their closure resulting from the healing of the very wound created for gaining access to the surgical site. In creating the egress by photoablation, less inflammation at the egress site is induced than by current techniques, thus prolonging filtration wound function.
(c) Vitreous Humor
The vitreous humor is that transparent portion of the eye between the lens/zonule diaphragm and the retina. It is attached to the retina and composed of a network of fibrils which, if stressed, can induce the retina to detach or wrinkle with subsequent loss of vision.
Treatment of diseases of the vitreous humor, including hemorrhage, membranes and foreign bodies, requires cutting devices which remove the diseased portions without stressing the attached fibrils to avoid retinal detachment. Current devices include mechanical micro-scissors and guillotine suction cutters, all of which produce vibration shocks in their actions. The advantage of applying photoablation to these tasks is the ability to remove this diseased tissue with less disruption of the local environs together with improved surgical control. Intra-vitreal photoablation is now possible with this fiberoptic device.
(d) Periocular Surgery
The lacrimal drainage system carries tears from the eye to the nasopharnx. Obstruction can occur from the eyelid punctum to the nasolacrimal duct.
Therapies currently employed include dilation approaches which often reclose and dacryocystorhinostomy in which a surgical window in created by removing bone and mucosa from an incision at the side of the nose. However, using photoablation, with a cannula under direct visualization, a flexible fiberoptic catheter is passed through the punctum to the site of the obstruction followed by the application of laser energy. Thus, photoablative removal of the obstruction precludes the necessity for surgical incision for bone removal, thereby greatly decreasing the morbidity and healing time.
(e) Laser Technology
Lasers were first used in 1965 to repair retinal detachment. The procedure involved chorioretinal coagulation in which a laser beam positioned from without the eye was used to achieve fusion of the retina and the choroid. See, for example U.S. Pat. No. 3,720,213 to Hobart et al, and U.S. Pat. No. 3,703,176 to Vassiliadas et al, wherein the techniques consisted of introducing a laser beam from outside the cornea, and by employing the refractive media of the eye itself, the laser radiation was directed in such a manner that it was concentrated at a selected point upon the retina/choroid so that the tissues in a very localized area were congealed.
In U.S. Pat. No. 4,207,894 to Choy and U.S. Pat. No. 4,469,098 to Davi are shown laser systems for performing coronary angioplasty and the like wherein a flexible fiberoptic probe is actually inserted into and through body tissue to impinge directly at the pathological site. However, both of these systems utilize high powered CO.sub.2 or Nd YAG lasers in which large amount of heat is generated to perform thermal excisions or to thermal vaporization of the tissue lattice.
U.S. Pat. No. 4,538,608 to Esperance shove a method and apparatus for removing cataractous lens tissue in the eye by either Neodymium-YAG (infrared-thermal) or excimer (ultraviolet) laser radiation, the laser beam again being introduced from without the eye and applied afocally or diffusely as it enters the eye through the cornea. Meyers U.S. Pat. No. 4,601,288 employs another externally introduced YAG laser device for focussing multiple laser pulses from a position outside the eye and passing the beam through the cornea to a point at the back surface of the lens in order to effect removal thereof.
U.S. Pat. No. 4,391,275 to Fankhauser et al and U.S. Pat. No. 4,558,698 to O'Dell relate to methods for surgical treatment of glaucoma by directing a YAG (Yttrium-Aluminum-Garnet) laser from outside the eye such that the laser beam passes through the cornea to focus upon the trabecular meshwork in the region of the irido-corneal angle. Reestablishment of the free circulation of the aqueous humor is enabled by laser perforation of the wall separating the anterior chamber of the eye from the canal of Schlemm on the level of the trabecular meshwork, or by opening the supra-choroidal space, or by perforating the iris.
In contrast to thermal energy produced by the infrared lasers, such as the Nd-YAG systems, the high photon energies of ultraviolet light can directly break chemical and biologic bonds without interacting with the material in question, namely eye tissue, in a manner as would cause temperature elevation. By photoablation, both ultraviolet and infrared radiation can be used to drastically alter the chemical behavior of a system in a "cold" environment. This becomes significant for controlled removal of organic substances, such as living tissue, in contradistinction to treatments in which heat is generated, e.g by thermal infrared lasers, which could damage, if not destroy, delicate eye tissue adjacent to the target sites to be removed. A problem associated with the use of ultraviolet radiation is that its emission could potentially injure the retina, or induce changes in DNA. Because UV radiation may be dispersed or conducted into surrounding portions of the eye without the use of fiber control, such UV treatment presented unacceptable risk in the past.
Excimer lasers form a group of pulsed high pressure gas lasers which emit at 193 nanometers (ArF.sup.e), 248 nm (KrF.sup.e), 308 nm (XeCl.sup.e) and 351 nm (XeF.sup.e) in the ultra-violet spectrum. In contrast to the thermal infrared radiation from some Nd-YAG or cO.sub.2 lasers or the like, the high energy UV photons from excimer lasers at photoablative fluence levels interact with the absorber molecules, leading to chemical bond breaking, ionization or electronic excitation. The present invention deals with the delivery of photoablative fluence levels of ultraviolet and infrared photons to the precise point of the target tissue of the eye by fiberoptic delivery systems without impinging upon the overlying or surrounding tissue or upon the tissue at the point of entry into the eye by the beam itself.